[scripts] add comment for remove_3d_attributes

Author: amin1377

vtr_flow/scripts/remove_3d_attributes.sh

@@ -1,5 +1,10 @@
 #!/usr/bin/env bash
 
+# This script is intended to be used on RR graph XML files generated by VPR.
+# If the architecture is a 2D architecture, you can simply call this script
+# to remove all attributes related to 3D FPGA support (layer="0",
+# layer_low="0", layer_high="0"). In VPR, these values default to 0.
+
 # Exit if any command fails
 set -e